The present invention concerns a disinfecting preparation containing chlorine in alcohol. More specifically, the invention relates to a liquid germicidal formulation containing, as the active ingredients, a combination of an alcohol and an organic N-chloroamine, which combination shows a high bactericidal activity and an unexpected stability in time, while maintaining its effectiveness substantially unchanged even after a prolonged storage.
The bactericidal properties of alcohols, known since ancient times, have been studied on a scientific basis starting from the beginning of this century. Some of such products, firstly ethyl alcohol and isopropyl alcohol, have reached in the field of disinfectants a quite remarkable diffusion, also in view of the advantages connected with their water solubility, with the ease of evaporation and with their reduced toxicity. Actually, some higher aliphatic alcohols are more effective than the lower ones as antimicrobial agents, the highest effectiveness being reached by alcohols having 6-8 carbon atoms. However, the low volatility and the unpleasant odor of these compounds have greatly limited their use. Also some aromatic alcohols find some limited application as disinfectants, among which benzyl alcohol and phenethyl alcohol. The latter, however, suffer from the disadvantage of being more toxic.
Ethanol shows its maximum potency as a 60-75% aqueous solution (weight percentage), while solutions of lower or even higher concentration take a longer time to exert the same germicidal effects. Both alcohols with three carbon atoms, i.e. n-propanol and isopropanol, show a higher activity than ethanol, with a maximum level at concentrations around 60% by weight. In spite of their unquestioned antibacterial activity, from the point of view of the activity spectrum aliphatic alcohols have the drawback of being totally ineffective against spore-forming micro-organisms.
Another product the use of which as disinfectant is well established since the last century is chlorine. Chlorine was employed, in the form of calcium chloride, for treating the sewage of the city of London in the mid-XIX century. In the same period, chlorine was used as a disinfectant in the hospital of Dr. Semmelweis in Vienna, to fight the puerperal fever. Although the mechanism of action of chlorine has not yet been fully clarified, it is believed that chlorine performs its disinfecting action by releasing in water hypochloric acid (HClO), which is responsible for the destruction of microorganisms. The concentrations of active chlorine required to kill most of the bacterial species may be of the order of 1 ppm, while higher concentrations are normally required to destroy spores and mycobacteria.
In the current practice, the term chlorine disinfectant is generically employed to refer to any disinfectant consisting in an aqueous solution of chlorine, hypochlorite or hypochlorous acid and also, in many cases, to other organic or inorganic chlorine-releasing compounds, such as, e.g., chloroamines (ClNH2, Cl2NH, Cl3N), N-chlorosulfonamides (e.g., sodium N-chloro-p-toluenesulfonamide or chloramine-T, and sodium N-chlorobenzenesulfonamide or chloramine-B), N-chloroisocyanuric acids. Such compounds are also employed, at the same time, in view of their activity as chemical oxidants, and are consequently the most widely used products for the treatment of drinking water, for sanitizing swimming pools and for water treatment in the food industry.
In view of the foregoing, the interest in formulating a disinfectant containing, as the active ingredients, both alcohol and chlorine is quite clear. A similar preparation would join the antiseptic properties typical of each one of these two classes of compounds, thereby resulting in a product with an enhanced potency and a wider activity spectrum. Although the known art includes many disinfectants that combine the antibacterial activity of alcohols with the activity of other agents, such as, e.g., iodine, phenols or chlorhexidine, no preparations consisting of combinations of chlorine and alcohol appear to be presently on the market. This is apparently due to the strong oxidizing action exerted by chlorine on such organic products, that are known to be relatively easily oxidizable.
As it is known, the power of a compound as an oxidant is measured on one hand by thermodynamic factors, in particular by the standard oxidation potential of the compound, and on the other hand by kinetic factors, which govern the rate of the oxidation reaction. As a matter of fact, although in the absence of information on the reaction kinetics it is impossible to precisely foresee the performance of an oxidizing system, a first valuable indication is always found in the standard oxidation potentials. It is, actually, the high standard oxidation potential for the reduction of molecular chlorine to chloride ion (Cl2+2exe2x88x922Clxe2x88x92) and that for the reduction of hypochloric acid to chloride ion (HOCl+H++2exe2x88x92  Clxe2x88x92+H2O)xe2x80x94 respectively, E0=1.36 V and E0=1.49 Vxe2x80x94that give the most immediate indication of the potency of the chlorine-based agents as chemical oxidants (see, e.g., R. G. Rice and M. Gomez-Taylor, Environmental Health Perspectives, 69, 31-44, (1986)).
In this connection, it has been shown experimentally (D. Coates and J. E. Death, Journal of Clinical Pathology, 31, 148-152, (1978)) that mixtures of various alcohols or glycols (i.e., methanol, n-propanol, isopropanol, ethanol and ethanediol) in aqueous solution at various concentrations (from 10 to 50% by weight) with sodium hypochlorite at a level of available chlorine of 2000 ppm, although having an interesting sporicidal activity when freshly prepared, had lost practically all available chlorine after few hours. In order to exploit the advantageous biological activity discovered, therefore, the concerned publication suggests to store the solutions of alcohol and hypochlorite in separate containers, and to mix them just before use.
A first measure aimed at limiting as much as possible the reactivity between alcohols and chlorine disinfectants may be to use, in a possible preparation, a chlorine source characterized by an oxidation potential lower than sodium hypochlorite, which is able to supply chlorine much more slowly than the common hypochlorites. Products particularly suitable to this end are the chloroamines, as it may be inferred from the following table. The table shows the standard oxidation potentials at 25xc2x0 C. in aqueous solution (according to two different literature references, i.e. a): R. G. Rice and M. Gomez-Taylor, loc. cit.; b): Ullmann""s Encyclopedia of Industrial Chemistry, 5th ed., VCH Verlagsellschaft A 28, 87 (1996)).
Although they are not as powerful as chlorine, chloroamines have the advantage of being more stable, since they are less rapidly reactive. In water, chloroamines slowly hydrolyze, generating hypochloric acid according to the general reaction RRxe2x80x2NCl+H2O  RRxe2x80x2NH+HOCl. In view of the fact that the bactericidal activity of these compounds is due to the release of hypochloric acid, the value of the equilibrium constant of the above reaction is used to express the activity of chloroamines as disinfectants. Since hypochloric acid is released gradually from these compounds, the latter may keep their disinfecting activity for longer periods of time, compared to hypochlorites.
Among the possible organic and inorganic compounds belonging to the family of chloroamines, the present invention is concerned with two specific agents, already mentioned in the foregoing, consisting in the monosodium salts of two N-chlorosulfonamides, i.e. N-chloro-p-toluenesulfonamide sodium salt or chloramine-T, 
and N-chlorobenzenesulfonamide sodium salt or chloramine-B 
Both these compounds are known as topical antiseptics and for water sterilization, as they are active against a wide spectrum of microorganisms.
EP 372415 disclosed a process for the stabilisation of Chloramine-T and -B solutions according to which oxidation-resistant buffers (HEPPS and BICIN) are used at pH between 7 and 12.
U.S. Pat. No. 3,767,586 discloses a process for preparing stable solutions of N-halo compounds by reaction of a N-hydrogen compound, a halogen, an alkali or alkaline earth metal hydroxide, the presence of a buffer at pH 4.5-8.5.
Block, S. S., xe2x80x9cDisinfection, Sterilisation and Preservation, Fourth Editionxe2x80x9d (Pg. 143), Lea and Febiger, Philadelphia, US, describes inorganic chloramines and their use as bactericidal agents, including chloramine-T, whose bactericidal action is obtained at law pH and with long exposure.
As for all of the other chlorine disinfectants, the use of chloramine-T and chloramine-B in alcohol-based formulations was not considered to be commercially possible according to the current practice, in view of the oxidizing activity exerted by chlorine on alcohols.
One only known patent publication, i.e. patent No. 2255 of the former German Democratic Republic, issued in 1943, discloses antiseptic formulations which are said to contain both a chlorosulfonamide and aliphatic alcohols. However, such preparations also contain an organic dye extremely prone to oxidation, e.g. naphthol yellow S or 2,4,4-trinitrophenol sodium salt. According to the document, the alcohol prevents the organic dye from being oxidized by chloramine. From the comparative tests reported in the patent, a solution of naphthol yellow dye and chloramine-T in distilled water heated at 40xc2x0 C. is rapidly degraded, as it is evidenced by the strong odor emanating from the solution, while a similar solution wherein 50% by volume of ethyl alcohol is present does not undergo any detectable odor changes. In the event that the temperature is kept at 50xc2x0 C. for 16 hours, the concentration of active chlorine in the water solution of dye and chloramine-T is reduced by 92% by weight, while the concentration of active chlorine in the solution containing 50% of alcohol is reduced by 4.5% by weight only. Such a reduction is in any case too marked to allow to consider a disinfecting product stable according to the current standards. In addition, the document does not supply any specific indication that may be used to obtain, in general, alcohol solutions of chloramine-T or -B of any desired concentration, which are stable for quite long periods of time. On the contrary, the document seems to suggest that any formulation based on N-chlorosulfonamide and a dye, mixed with alcohols, may behave as a stable solution (within the limits inferrable from the example referred to above).
On the contrary, it has been found, according to the present invention, that a hydroalcoholic solution of chloramine-B or chloramine-T may remain stable for periods of time of several months, losing amounts of active chlorine of no more than few units per cent, provided that the pH of the solution is kept above 8.5, preferably above 9.5. The critical influence of pH may be explained if one considers that chloramines B and T, being strong electrolytes, readily dissociate in aqueous solution, thus transforming into the corresponding anionic form: 
(wherein X may be a hydrogen atom or the xe2x80x94CH3 group). In view of the markedly basic character of such species, it is expected that the attack by protons possibly present in the solution takes place quite easily through an acid-base equilibrium. Considering that the active species in the alcohol oxidation reaction is likely to be the protonated species, it may be understood that the pH can exert a great influence on the said reaction, hindering the reaction as much as the proton concentration is low.
In order to give an experimental confirmation of the above hypothesis, made in the frame of the invention, the following table shows the percent amount of available chlorine measured in aqueous solutions containing 60% by weight isopropanol and 10 g/l chloramine-B (equivalent to 2500 ppm of active chlorine), as well as various phosphate buffers, depending on the desired pH, the solution being kept at 40xc2x0 C. for 4 weeks.
The data presented in the above table show that beyond a limit of pH close to 8.5 the stability of chlorine in time drastically increases. Above the concerned limit, the oxidation-reduction reaction of chloramine with alcohol appears to proceed extremely slowly, leaving practically unaltered the concentration of available chlorine.
Accordingly, the present invention specifically provides a disinfecting preparation containing chlorine in alcohol solution comprising, in water, chloramine-T or chloramine-B as defined above, and one or more aliphatic alcohols having up to 12 carbon atoms, said solution having a pH not lower than 8.5. Preferably, the said desired pH value is maintained in the disinfecting preparation by means of a suitable buffer.
In order to perform its germicidal activity at the level normally required to a disinfecting agent, the formulation according to the invention contains said chloramine-T or said chloramine-B at a concentration corresponding to 1000-2500 ppm of available chlorine, the optimal concentration being around 1100-1150 ppm of available chlorine. By way of example, a composition according to the invention containing 0.5% by weight of chloramine-T contains about 1120 ppm of active chlorine.
Preferably, the aliphatic alcohols are chosen from ethanol, n-propanol and isopropanol, and are present at a total concentration comprised between 40 and 70% by weight. It has been experimentally ascertained that the stability of chlorine in the solution according to the invention, measured by the percentage of available chlorine and referred to the starting concentration, after storage at a fixed temperature for a given period of time, is slightly higher for isopropanol solutions than for ethanol solutions. This finding, together with the already mentioned higher bactericidal activity of isopropyl alcohol compared with ethyl alcohol, makes isopropyl alcohol a preferred ingredient in the disinfecting formulations according to the invention.
In addition to possessing a high disinfecting power towards a wide spectrum of microorganisms and, moreover, a considerable sporicidal activity, the proposed preparation has also the property of removing any residues of adhesive tape. The latter is a quite important property in view of the use of the disinfecting product in out-patient treatment centers, in blood collection centers and in hospital departments, and cannot be obtained with alcohol-based disinfectants. Such property is a consequence, in the preferred embodiments of the invention, of the presence of a borate buffer in the composition. The borate buffer performs, on one hand, the function of maintaining the pH at the high levels desired (as the system H3BO3/H2BO3xe2x88x92 has a pK of about 9.2 at 25xc2x0 C., and thus has a buffering pH between 8 and 10) and, on the other hand, enhances the removal of any tape adhesive that may be present on the patient""s skin. It is known, actually, that borate ion can remove the residues of the rubber adhesives currently used in adhesive medications and plasters.
The inclusion of the system boric acid/sodium hydroxide in the disinfecting formulation according to the invention also has the advantage of adding the two functions referred to above without interfering in any way with the system chloramine-alcohol, and without affecting the stability of such system. Comparative tests have evidenced that among the other possible agents able to give a good removal of the adhesive, such as, e.g., benzyl alcohol and dichloromethane, the borate buffer is able to assure the highest stability of chlorine. In addition, dichloromethane would bring about unacceptable toxicity problems for a disinfecting product for topical use as the one proposed herein.
The concentration range of the borate buffer that allows to obtain the maximum stability is quite limited, owing to the possibility of precipitation of sodium borate. Precipitation may occur, in particular, at low temperatures and in presence of an excess of sodium ions. Specifically, the optimal weight concentrations of the components of borate buffer in the formulation according to the invention are the following:
Thus, some particularly advantageous embodiments of the invention have the following parameters:
Preferably, the chloramine is chloramine-T, at a concentration corresponding to 1100-1150 ppm of available chlorine, and the alcohol is isopropanol, at a concentration of 50% by weight. The pH of such preferred formulations is between 10.4 and 10.9. In order to achieve the maximum chlorine stability in the storage of the product for periods of time of at least several months, the preparation should be packaged in opaque containers, preferably dark, in order to avoid that the oxidation of alcohol is catalyzed by the electromagnetic radiation.
Some specific embodiments of the disinfectant formulation of the invention are described below for merely illustrative purposes, together with the results of the experimental studies carried out on the said formulation.